1. Field of the Invention
This invention relates to a noise suppressing device, and more particularly to a common mode noise suppressing device.
2. Description of the Related Art
A conventional common mode noise suppressing device is mainly implemented with lumped elements, and usually uses characteristics of a symmetric differential transmission line whose intermediate potential is equivalently grounded. Thus, the conventional common mode noise suppressing device may provide two differential transmission paths, each of which is implemented with an inductively coupled all-pass filter or a low-pass filter.
However, when the inductively coupled all-pass filters are used, two electromagnetically coupled inductors are required in each differential transmission path while self-inductances and a mutual inductance of the inductors are required to be finely tuned so as to meet a required frequency response. Therefore, design of the conventional common node noise suppressing device is troublesome and time-consuming. On the other hand, when the low-pass filters are used, the conventional common mode noise suppressing device may have a limited operating frequency range.